Step-closing pressing of medium density fiberboard; Part 1. Influences on the vertical density profile

Abstract

Medium density ®berboard (MDF) is one of the most rapidly growing composite board products available in the market. A key product attribute of MDF is the density pro®le through the panel thickness. A superior MDF panel for laminating, gluing and ®nishing should have an unbalanced density pro®le, in which the face density is considerably higher than the core density. The homogeneous core of MDF makes it especially suitable for embossing, moulding, and general machining. A uniform density throughout the panel thickness results in better fastening properties. A step-closure schedule to change the density pro®le of lab-made MDF panels is presented. MDF mats were pressed using eight different step-closure schedules. Our in-press density monitoring system was used during pressing to provide additional information about the formation of the density pro®le. The effects of step-closure on the density pro®le formation are discussed. The step-closure schedules signi®cantly changed the traditional shape of the vertical density pro®le of the laboratory, made MDF panels. The step-schedules resulted in multiple densi®cation peaks rather than the traditional two peaks associated with conventional pressing. The stepschedules resulted in increased core density, which was greater than the face density. Comparison is made to traditional MDF closing schedules and OSB step-closing schedules. Schrittweises Pressen von mitteldichten Faserplatten(MDF); Teil 1. Einfluû der vertikalen Dichteprofile Eine Schlu Èsseleigenschaft von MDF ist das Dichtepro®l quer zur Dicke der Platte. Eine hochwertige MDF-Platte fu Èr Beschichtung, Verleimung und andere Ober¯a Èchen-handlungen sollte kein gleichma Èûiges Dichtepro®l aufweisen, sondern die Dichte nahe der Ober¯a Èche sollte wesentlich ho Èher sein als die Kerndichte. Die homogene Kernschicht von MDF macht diese besonders geeignet fu Èr Bearbeitungen aller Art. Fu Èr die Herstellung von Laborplatten mit verschiedenen Dichtepro®len wurden acht verschiedene La Èufe mit schrittweiser Pressung untersucht. Die Plattendichte wurde mit einem speziellen System online wa Èhrend der Pressung gemessen, um zusa Ètzliche Informationen u Èber die Ausbildung der Dichtepro®le zu erhalten. Die Ein¯u Èsse der verschiedenen Preûmethoden auf die Dichtepro®le wird diskutiert. Es ergab sich eine wesentliche A È nderung der traditionell bekannten Form der Dichtepro®le. Der wesentliche Unterschied besteht im Auftreten von mehreren Dichtepeaks gegenu Èber nur zwei Peaks bei der konventionellen Pressung. Auûerdem ist die Kerndichte erho Èht; sie liegt zum Teil sogar ho Èher als die Ober¯a Èchendichte. Die neue Methode wird mit den bisher angewandten Preûverfahren verglichen.

Multivariate modeling of MDF panel properties in relation to wood fiber characteristics

“…The pressing schedule and platen temperature are critical, since these factors can result in significant differences in the panel vertical density profile (VDP), which largely determines the physical and mechanical properties of panels (Suchsland and Woodson 1974;Kelly 1977;Harless et al 1987;Winistorfer et al 1996;Wang et al 2001Wang et al , 2004. VDP can be determined by the pressing schedule and platen temperature used for panel consolidation (Andrews et al 2001;Wang et al 2001). The VDP is closely related to the strength and physical properties of composite panels (Suchsland and Woodson 1974;Kelly 1977;Harless et al 1987;Winistorfer et al 1996;Wang et al 2001Wang et al , 2004.…”

“…VDP can be determined by the pressing schedule and platen temperature used for panel consolidation (Andrews et al 2001;Wang et al 2001). The VDP is closely related to the strength and physical properties of composite panels (Suchsland and Woodson 1974;Kelly 1977;Harless et al 1987;Winistorfer et al 1996;Wang et al 2001Wang et al , 2004. The shape of the VDP curve is of importance.…”

Determining thermal physical properties of pyrolyzing New Zealand medium density fibreboard (MDF)

“…As a by-product of the manufacturing process, MDF has a non-uniform density profile along the panel thickness, so called vertical density profile (VDP), which is mainly formed from the heat and pressure applied simultaneously to the panel surfaces during the hot pressing process (Gupta, 2007;Wang et al, 2001). In general, the surface density is considerably higher than the core density whereas the core is relatively more homogenous (Wang et al, 2001;Ayrilmis, 2007).…”

“…As a by-product of the manufacturing process, MDF has a non-uniform density profile along the panel thickness, so called vertical density profile (VDP), which is mainly formed from the heat and pressure applied simultaneously to the panel surfaces during the hot pressing process (Gupta, 2007;Wang et al, 2001). In general, the surface density is considerably higher than the core density whereas the core is relatively more homogenous (Wang et al, 2001;Ayrilmis, 2007). The development of the VDP due to the hot pressing process has been investigated by many researchers with several theoretical and mathematical models developed (Harless et al, 1987;Suo and Bowyer, 1994;Wang and Winistorfer, 2000;Gupta et al, 2007;Thoemen and Humphrey, 2003;Thoemen and Ruf, 2008).…”

A simplified model on vertical density profile and shrinkage ratio of virgin and charred medium density fibreboard

“…Density is one of the most important and fundamental properties due to its predominant effects on both mechanical and thermal processes during pyrolysis. A manufactured MDF panel should have an unbalance density profile along its thickness, so called vertical density profile (VDP), which is mainly formed from the heat and pressure applied simultaneously on the panel surfaces during the hot‐pressing process . Generally, the surface density is considerably higher than the core density whereas the core is relatively more homogenous .…”